There are presently known solid-state RF switches which are utilized to control, switch or redirect RF energy in various applications, such as radar signals, and RF commutators. Those presently available solid-state RF switches, although faster than mechanical commutators, are too slow. In many applications, it is required to commutate the RF signal from one port to another in a time frame of less than 30 microseconds.
For example, in those applications where it is desired to switch off an RF transmitter and to turn on an RF receiver in less than a millisecond, the present solid state switches are unable to switch quickly enough.
The presently available RF solid-state switches do not provide enough isolation when the load to which RF energy is directed has a poor VSWR (Voltage Standing Wave Ratio) that is; the load is not properly terminated with the correct impedance. When such switches are used to switch between antennas or filters, it is impractical to assume that these elements are all properly terminated under all conditions. As a result, it is common to use a heavier-duty switch which is power overrated to maintain sufficient isolation, but at considerable cost in terms of the system that the switch is utilized in. However, even using an overrated switch will not withstand a short or an open circuit, and thus will fail to maintain isolation between ports and cause unwanted cross-talk.
An additional problem in present solid-state RF switches is that the RF energy is transmitted in a direct path through PIN diodes. Unfortunately PIN diodes are non-linear devices and accordingly, there is a significant amount of unwanted signal produced such as second, third and higher order intermodulation products and harmonics, which distorts and otherwise degrades the desired RF signal.
The present solid-state RF switches require high voltage to operate. Typically voltages higher than 100V or several 1000 may be required. The prior art switches also cannot switch without some sort of ringing and annoying amplitude shaping caused by the present architecture.
Finally, presently available solid-state RF switch architectures do not perform well in broadband applications and perform better in a narrow band environment, with all the difficulties mentioned above still being present. In order to provide a response to wider signal band, multiple solid-state RF switches must be employed.